This is a complete revision guide for AQA Combined Science Physics Paper 2 (specification code 8464), covering Topics 6.5 to 6.7: Forces, Waves, and Magnetism and Electromagnetism. This guide is written specifically for Combined Science students. If you are sitting Triple Science Physics, a separate guide is available for that specification. Content labelled Higher Tier only is for Higher students. Foundation students can skip those sections.
Do not read this passively. After each section, cover the page and try to recall the key equations and points from memory. Use the exam tips and common mistakes to sharpen your technique alongside your content.
Work through each topic in order. After reading a section, close the page and recall the key points and equations from memory. Focus extra time on any area where your recall is weakest before the exam.
Topic 6.5: Forces
Scalars and vectors
A scalar quantity has magnitude only and no direction. Examples include mass, time, temperature, energy and speed. A vector quantity has both magnitude and direction. Examples include force, velocity, acceleration and displacement. Vectors are drawn as arrows where the length represents the size and the direction of the arrow shows the direction of the quantity. If the direction of a quantity changes, the vector changes even if the size stays the same. A car going round a circle at constant speed has a changing velocity because its direction is continuously changing.
Contact and non-contact forces
A force is a push or pull caused by an interaction between objects. Forces always occur due to interactions and never in isolation.
Require physical contact: friction (opposes motion between surfaces), air resistance (drag in air), tension (force in a stretched rope or string), normal contact force (support from a surface).
Act at a distance: gravity (attraction between masses), electrostatic force (between charged objects), magnetic force (between magnets and magnetic materials).
Gravity and weight
Gravity is a non-contact force of attraction between masses. The Earth creates a gravitational field and any mass in this field experiences a gravitational force.
Where W is weight in newtons, m is mass in kilograms and g is gravitational field strength in N/kg. On Earth g is approximately 9.8 N/kg. On the Moon g is approximately 1.6 N/kg. Weight depends on location. Mass is the amount of matter in an object and is constant everywhere, regardless of location. Weight acts at the centre of mass and is measured using a Newton meter.
Resultant forces
The resultant force is the single force that has the same effect as all forces acting on an object combined. If the resultant force is zero, the object is in equilibrium and stays at rest or continues at constant velocity. If the resultant force is not zero, the object accelerates or changes direction. Forces in the same direction are added. Forces in opposite directions are subtracted.
Higher Tier only: a free body diagram shows all forces acting on a single object with arrows drawn from a point. Only forces acting on the object are included, not forces the object exerts on others. A single force can also be resolved into a horizontal component and a vertical component, which is useful in slopes, projectile and equilibrium problems.
Work done and energy transfer
Work is done when a force causes movement in the direction of the force. If there is no movement, no work is done regardless of the size of the force. One joule equals one newton of force moving an object one metre. Work done equals energy transferred. Friction converts kinetic energy into thermal energy, which is why brakes heat up and rubbing hands together produces warmth.
Forces and elasticity: Hooke's Law
Elastic deformation means the object returns to its original shape when the force is removed. Inelastic deformation leaves a permanent change.
Where F is force in newtons, k is the spring constant in N/m and e is extension in metres. A high spring constant means a stiff spring. A low spring constant means a soft spring. Hooke's Law only applies up to the limit of proportionality, beyond which the force-extension graph curves and the relationship is no longer linear. Elastic potential energy is stored in a stretched or compressed spring.
Required Practical 18: Hooke's Law
Aim: investigate the relationship between force and extension of a spring. Hang a spring vertically, measure its original length, add masses gradually and record the extension at each step. Plot force against extension. The straight-line region confirms Hooke's Law and the gradient equals the spring constant k. Sources of error include parallax when reading the ruler and the spring oscillating. Waiting for the spring to reach equilibrium before each reading improves accuracy.
Forces and motion
Distance is the total path length and is a scalar. Displacement is the shortest straight line from start to finish and is a vector. Speed is a scalar. Velocity is speed in a specific direction and is a vector. On a distance-time graph, gradient equals speed. On a velocity-time graph, gradient equals acceleration and the area under the graph equals the distance travelled. Terminal velocity occurs when weight equals air resistance, the resultant force is zero and the object stops accelerating.
Newton's Laws of Motion
- Newton's First Law: if the resultant force is zero, an object stays at rest or continues at constant velocity
- Newton's Second Law: F = ma. Acceleration increases with force and decreases with mass.
- Newton's Third Law: whenever two objects interact, the forces are equal in size and opposite in direction. These forces act on different objects, not the same one.
Required Practical 19: force and acceleration
Aim: investigate the effect of force on acceleration and the effect of mass on acceleration. Use a trolley on a runway with a pulley and light gates to measure acceleration. Varying the hanging mass changes the force. Varying the trolley mass tests the effect of mass. Results confirm that acceleration is proportional to force and inversely proportional to mass, which confirms F = ma.
Stopping distance
Total stopping distance equals thinking distance plus braking distance. Thinking distance is the distance travelled during the driver's reaction time and increases with speed. Braking distance is affected by speed, vehicle mass, road conditions and brake condition. During braking, work done by friction converts kinetic energy into thermal energy. Large decelerations produce high forces on passengers, cause brake overheating and can cause loss of vehicle control.
Momentum (Higher Tier only)
In a closed system, total momentum before equals total momentum after. Momentum is conserved in all collisions and explosions. Airbags and crumple zones increase the time over which momentum changes, which reduces the force on passengers and reduces injury risk.
Topic 6.6: Waves
Transverse and longitudinal waves
Waves transfer energy without transferring matter. In transverse waves, vibrations are perpendicular to the direction of energy transfer. Examples include water waves and all electromagnetic waves. Transverse waves have crests and troughs. In longitudinal waves, vibrations are parallel to the direction of energy transfer. Sound waves are longitudinal. Longitudinal waves have compressions (particles close together) and rarefactions (particles spread out). It is the energy of the wave that moves, not the particles themselves.
Properties of waves
Amplitude is the maximum displacement from the rest position and is related to the energy of the wave. A bigger amplitude means more energy. Wavelength is the distance between identical points on the wave, such as crest to crest. Frequency is the number of waves passing a point per second, measured in hertz. Period is the time for one complete wave. When a wave moves from one medium to another, its frequency stays the same but its speed and wavelength both change.
Required Practical 20: waves in a ripple tank or solid
Aim: investigate frequency, wavelength and speed of waves. In a ripple tank, generate waves using a dipper, measure wavelength from the pattern below the tank, count the number of waves passing per second to find frequency, and calculate wave speed using v = f times lambda. Higher frequency gives a shorter wavelength. Wave speed stays constant within the same medium. Common errors include parallax when measuring wavelength and inconsistent wave production.
Electromagnetic spectrum
All electromagnetic waves are transverse and travel at 3 times 10 to the power of 8 metres per second in a vacuum. They do not need a medium to travel. In order of increasing frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Higher frequency means shorter wavelength and higher energy.
| Type | Uses | Risks |
|---|---|---|
| Radio waves | TV and radio broadcasting | Low risk |
| Microwaves | Cooking, satellite communication | Internal heating of tissue |
| Infrared | Heaters, thermal imaging | Skin burns |
| Visible light | Vision, fibre optics | Eye damage at high intensity |
| Ultraviolet | Sterilisation, security marking | Skin cancer, sunburn |
| X-rays | Medical imaging | Cell mutation, cancer risk |
| Gamma rays | Cancer treatment, sterilisation | Most dangerous, deep tissue damage |
When explaining why each wave type is suitable for a particular use, always refer to its wavelength, penetration, energy level and whether it is absorbed or transmitted by the relevant material.
Reflection, absorption and transmission
Different materials can absorb, reflect or transmit electromagnetic waves. Dark, dull surfaces absorb more infrared radiation. Light, shiny surfaces reflect infrared. Refraction occurs when a wave changes speed as it enters a different medium, causing it to change direction. In a faster medium, the wavelength increases. In a slower medium, the wavelength decreases. All electromagnetic waves can reflect, refract, be absorbed or be transmitted.
Required Practical 21: infrared radiation and surfaces
Aim: investigate how infrared absorption and emission depend on surface type. Place containers with different surfaces (matt black and shiny silver) filled with hot water. Measure the temperature change over time. Black surfaces absorb and emit infrared radiation well and cool or heat faster. Shiny surfaces reflect infrared and are poor absorbers and emitters.
Topic 6.7: Magnetism and Electromagnetism
Permanent and induced magnets
Every magnet has a north-seeking pole and a south-seeking pole. Like poles repel and unlike poles attract. Magnetic force is a non-contact force. A permanent magnet always produces its own magnetic field. An induced magnet only becomes magnetic when placed in a magnetic field and loses its magnetism when removed. Induced magnetism always causes attraction, never repulsion. Magnetic materials include iron, nickel, cobalt and steel.
Magnetic fields
A magnetic field is a region where a magnetic force acts on a magnet or magnetic material. Magnetic field lines go from north to south, never cross and are strongest where they are closest together. The field is strongest at the poles and weaker further away. A compass needle is a small magnet that aligns with magnetic field lines. The Earth acts like a giant magnet and a compass points towards magnetic north. Students should be able to draw field patterns around bar magnets and describe the Earth's magnetic field.
Electromagnetism
When current flows through a wire, a circular magnetic field is produced around it. Increasing the current increases the field strength. Moving further from the wire decreases the field strength. A solenoid is a coil of wire that produces a stronger, more uniform magnetic field than a single straight wire. Adding an iron core increases the field strength and creates an electromagnet. An electromagnet can be switched on and off and its strength can be adjusted by changing the current.
The motor effect (Higher Tier only)
A force is produced when a current-carrying conductor is placed in a magnetic field. This is the motor effect. Fleming's Left-Hand Rule predicts the direction of force: the first finger points in the direction of the magnetic field (north to south), the second finger points in the direction of conventional current, and the thumb points in the direction of the force (motion).
Where F is force in newtons, B is magnetic flux density in tesla, I is current in amperes and l is the length of wire in the field in metres. Force increases with a stronger magnetic field, higher current or longer wire in the field.
Electric motors (Higher Tier only)
A coil carrying current in a magnetic field experiences forces on opposite sides, creating a turning effect (moment) that causes the coil to rotate. The split-ring commutator reverses the current every half turn to keep the coil rotating in the same direction. Brushes maintain electrical contact with the spinning commutator. The motor converts electrical energy into kinetic energy.
Saying induced magnets can repel: induced magnetism always causes attraction only. Mixing up the fingers in Fleming's Left-Hand Rule: first finger is field, second is current, thumb is force. Forgetting the commutator reverses current to maintain rotation direction. Confusing a solenoid with a single wire: a solenoid produces a much stronger and more uniform field.
Quick reference: all equations for Physics Paper 2
- Weight: \(W = mg\)
- Work done: \(W = Fs\)
- Hooke's Law: \(F = ke\)
- Elastic potential energy: \(E_e = \frac{1}{2}ke^2\)
- Speed: \(v = \frac{s}{t}\)
- Acceleration: \(a = \frac{\Delta v}{t}\)
- Uniform acceleration: \(v^2 - u^2 = 2as\)
- Newton's Second Law: \(F = ma\)
- Momentum (HT): \(p = mv\)
- Wave speed: \(v = f\lambda\)
- Period: \(T = \frac{1}{f}\)
- Motor effect force (HT): \(F = BIl\)
Most common exam mistakes across all three topics
- Confusing scalars and vectors: velocity and displacement are vectors, speed and distance are scalars
- Saying weight and mass are the same: mass is constant everywhere, weight depends on gravitational field strength
- Applying Hooke's Law beyond the limit of proportionality
- Saying no work is done when a force is applied but there is no movement: this is correct, but students often miss that the distance must be in the direction of the force
- Confusing Newton's Third Law force pairs: the two forces act on different objects, not the same one
- Confusing transverse and longitudinal waves: sound is longitudinal, light is transverse
- Saying particles move with the wave: energy is transferred, not matter
- Writing "orange to clear" for the wrong question: in this topic, writing "colourless" matters for EM wave absorption questions
- Saying induced magnets can repel: induced magnetism always causes attraction
- Using the wrong fingers in Fleming's Left-Hand Rule
- Forgetting the commutator's role in keeping motor rotation in one direction
- Saying a solenoid and a straight wire produce the same field: a solenoid produces a much stronger and more uniform field
